1. Field of the Invention
The present invention relates to a control method for a four-way valve of a multiple heat pump, and more particularly, to a control method for a four-way valve of a multiple heat pump which controls operation of four-way valves showing switching error to a cooling or heating mode, thereby ensuring normal operation of the four-way valves.
2. Description of the Related Art
FIG. 1 is a schematic diagram illustrating a refrigeration cycle of outdoor units provided in a conventional multiple heat pump system. Here, the conventional multiple heat pump system includes three outdoor units A, B and C.
Each of the outdoor units A, B and C comprises a compressor 10 that supplies a high-temperature and high-pressure gas refrigerant, a four-way valve 20 that switches refrigerant flow for use in a cooling or heating mode, an outdoor heat exchanger 30 that serves as a condenser to condense the refrigerant when an indoor heat exchanger acts as a cooler and also serves as an evaporator to evaporate the refrigerant when the indoor heat exchanger acts as a heater, and an expander 40 that expands the refrigerant to a low-temperature and low-pressure refrigerant.
When the heat pump system operates in a cooling mode, the gas refrigerant, compressed in the compressor 10, is introduced into a high-pressure portion 21 of the four-way valve 20 after passing through a certain element, such as an oil separator. Then, the gas refrigerant is introduced into the outdoor heat exchanger 30 via a connecting portion 22, thereby being condensed in the outdoor heat exchanger 30. After that, the refrigerant is supplied to an indoor unit by successively passing through the expansion valve 40 and a refrigerant pipe 41.
The gas refrigerant, evaporated while passing through an indoor heat exchanger, is returned to a suction port of the compressor 10 after passing through a connecting portion 23 and a low-pressure portion 24 of the four-way valve 20 via a refrigerant pipe 45.
On the contrary, when the heat pump system operates in a heating mode, the gas refrigerant, discharged from the compressor 10, successively passes through the high-pressure portion 21 and the connecting portion 23 of the four-way valve 20, and then is supplied into the indoor unit via the refrigerant pipe 45. After being condensed in the indoor heat exchanger, the resulting liquid refrigerant is introduced into the outdoor unit via the refrigerant pipe 41 and is expanded while passing through the expansion valve 40. In succession, the refrigerant is evaporated in the outdoor heat exchanger 30, and is introduced into the suction port of the compressor 10 by successively passing through the connecting portion 22 and the low-pressure portion 24 of the four-way valve 20.
In the multiple heat pump air conditioning system having two or more heat pump systems operating as stated above, the four-way valves 20 of the respective outdoor units are controlled to keep the same refrigerant channel switching manner as one another in the cooling or heating mode.
That is, in the cooling mode, all of the four-way valves 20 are switched to keep a cooling position as shown in FIG. 1, while, in the heating mode, all of the four-way valves 20 are switched to keep a heating position in an opposite direction of FIG. 1.
Especially, in order to switch the four-way valves 20, kept at the cooling position, to the heating mode, at least one of the compressors 10 of the respective outdoor units has to be driven to generate high and low pressures at the associated outdoor unit, so that the four-way valves 20 of the respective outdoor units are able to be switched using a pressure difference.
Switching manners of the four-way valves 20 are basically classified into two manners. A first switching manner is a low-pressure connection manner that connects the low-pressure portion 24 to both pressure-transmission holes 25 and 26 located at opposite sides of the low-pressure portion 24. If the low-pressure portion 24 is connected to one of the pressure-transmission holes 25 and 26, i.e. left pressure-transmission hole 25, a slider, disposed in each of the four-way valves, moves leftward to the heating position. Conversely, if the low-pressure portion 24 is connected to the other one, i.e. right pressure-transmission hole 26, the slider moves rightward to the cooling position as shown in FIG. 1.
Movement of the slider of the four-way valve 20 as stated above requires a minimum operating differential pressure. The operating differential pressure is produced upon driving of the compressor 20.
A second switching manner is a high/low pressure connecting manner that connects the high-pressure portion 21 to the left pressure-transmission hole 25 and the low-pressure portion 24 to the right pressure-transmission hole 26. The second switching manner is effective to readily move the slider of the four-way valve 20 as compared to the first switching manner since it produces high and low pressures at opposite sides.
Therefore, in order to switch the four-way valves 20 of the respective outdoor units A, B and C, after driving the compressors 10, the sliders, disposed in the respective four-way valves 20, move to the cooling or heating position when a predetermined operating differential pressure is produced, completing switching of the four-way valves 20 to the cooling or heating position.
Here, instead of simultaneously completing switching of the three four-way valves 20, as shown in FIG. 2, two four-way valves may be switched to the heating position, but the remaining four-way valve may not be completely switched from the cooling position to the heating position. In this case, since high-pressure producing portions 23H, connected to the high-pressure portions 21 of the outdoor units B and C, are connected to a low-pressure producing portion 23L of the outdoor unit A via a refrigerant pipe 45a, the low-pressure producing portion 23L of the outdoor unit A undergoes a pressure rising to thereby reach the same state as a high-pressure producing portion 22H of the outdoor unit A.
On the contrary, the high-pressure producing portion 22H of the outdoor unit A is connected to the outdoor units B and C via a high/low pressure connecting pipe 50, causing the refrigerant to flow to the low-pressure producing portions 22L that serve as connecting portions.
Continuation of such a state makes it impossible to switch the four-way valve 20 of the outdoor unit A using the conventional four-way valve switching manners when the outdoor unit A malfunctions.
Therefore, when the four-way valve 20 of one of the outdoor units provided in the multiple heat pump falls into a switching error, this makes it impossible normal cooling/heating operations of the multiple heat pump, and may cause damage to the multiple heat pump when the heat pump is continuously operated in the switching error state. Especially, such a malfunction problem of the outdoor unit cannot be solved by simply repeatedly operating the multiple heat pump.